This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We aim to employ the technique of picosecond time-resolved Laue crystallography to study biophysical processes in proteins. Specifically, we will use intense, short-duration laser pulses to trigger a structural change in a protein crystal, and will probe its structural evolution with single X-ray pulses isolated from the synchrotron pulse train using a sequence of X-ray shutters. By acquiring diffraction data at a well-defined instant in time after laser photolysis, we can construct a snapshot of the protein?s structure with time resolution limited only by the duration of the X-ray pulse, which is of the order of 100 ps. We aim to address numerous biophysical questions including the functional role of highly conserved residues in proteins, pathways for ligand migration to and from the protein?s active site, and the correlated structural changes that mediate or control allosteric regulation. To obtain the highest quality data possible, we will focus initially on protein systems whose structural changes are reversible. Ligand-binding heme proteins, including myoglobin and hemoglobin, are ideal model systems for these biophysical investigations. When CO is used as a surrogate for O2, the ligand can be photodissociated from the heme with high quantum efficiency, thereby triggering a sequence of events that can be studies structurally. Because the dissociated ligands rebind to the heme bimolecularly on the ms time scale, the structure returns to its starting state and the process can be repeated thousands of times. Thus, these model systems are ideal for pursuing these biophysical studies.